Biologically active phosphotriester-type nucleosides and methods for preparing same

ABSTRACT

Compounds of formula RS--P(═O) (QR)--Nu where: R is a radical --(CH 2 )n-W--X; X is a radical --C(═Z) (Y) or --S--U; Z is O or S; W is O or S; Q is O or S; Y and U are an alkyl, aryl or saccharide radical which is optionally substituted with, for example, an OH, SH or NH group; n is equal to 1 to 4, preferably 1 or 2; and Nu is a radical consisting of a residue of a biologically active compound or the dephosphorylated residue of a compound which is biologically active when it bears a phosphate or phosphonate group.

RELATED APPLICATION

This patent application is continuation-in-part of application Ser. No.08/416,515, filed Apr. 4, 1995 (now U.S. Pat. No. 5,770,725), which is acontinuation-in-part of application Ser. No. 08/343,433, filed on Nov.23, 1994 (now abandoned), which is the U.S. national phase ofInternational patent application PCT/FR93/00498, filed on May 24, 1993(now abandoned). The entire contents of each of the foregoing patentapplications is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the bioreversible functionalization ofphosphate or phosphonate groups of biologically active compounds.

The present invention relates more particularly to phosphotriester-typebiologically active compounds bearing phosphate or phosphonate groupswhich are protected by protecting groups that are bioreversible in anintracellular medium.

BACKGROUND OF THE INVENTION

Compounds bearing a phosphate or phosphonate group have a negativelycharged ionic nature and a physiological pH. As a result, thetherapeutic activity of such compounds is limited by the low diffusionof negatively charged compounds across biological lipid membranes.Moreover, compounds bearing phosphate groups are readilydephosphorylated by the action of phosphatase enzymes in the blood or oncell membranes, which enzymes dephosphorylate substrate compounds. Ingeneral, charged phosphate or phosphonate compounds are poorly absorbedvia oral administration, and do not diffuse efficiently across ellmembranes or even the cerebral barrier, which are lipidic in nature.

Certain compounds, such as nucleoside derivatives or analogs, are activeagents that are administered in nonhosphorylated form, but arephosphorylated in vivo in the form of metabolic monophosphate ortriphosphate to become active.

Thus, nucleoside derivatives having antitumor activity, such as5-fluorouridine, 5-fluoro-2'-deoxyuridine or1-O-D-arabinofuranosylcytosine, exert their activity in phosphorylatedform.

Similarly, in order to exert their antiproliferative activity, certainnucleoside or phosphononucleoside analogs need to be phosphorylated intothe corresponding triphosphate thereof by cellular or viral enzymes;this triphosphate is then capable of inhibiting the viral and/orcellular polymerases.

Among the various structural classes of antiviral agents,2',3'-dideoxynucleosides are among the most effective compounds in thetreatment of AIDS. However, these nucleoside analogs must undergo abiotransformation by cell kinases in order to exert their activity onthe replication of HIV, the etiological agent of AIDS. Thismetabolization occurs via the dideoxynucleoside 5'-monophosphate andthen the 5'-diphosphate to lead to the 5'-triphosphate, which is aninhibitor of HIV reverse transcriptase and which thereby interferes withthe biosynthesis of viral DNA.

Despite their great therapeutic potential, 2',3'-dideoxynucleosidessuffer from limitations, in particular the low metabolizability of someof them by kinases into triphosphate. 2',3'-Dideoxyuridine5'-triphosphate, for example, is an excellent inhibitor of reversetranscriptase (Z. Hao et al., Proc. Am., Assoc. Cancer Res., 1988, 29,348, E. Matthes et al., Biochem. Biophys. Res. Commun, 1987, 148,78-85). However, the nucleoside thereof is able to inhibit thereplication of HIV in vitro. Studies have shown that this result islinked to the low metabolizability of the nucleoside into itsmonophosphate by cell kinases (Z. Hao et al. Mol. Pharmacol. 1990, 37,157-153).

Thus, AZT is successively metabolized into the triphosphate thereof(AZTP), which is a potent inhibitor of HIV reverse transcriptase.Similarly, Acyclovir (ACV) is converted into the triphosphate thereof(ACVTP), which selectively inhibits herpesvirus DNA polymerase. Thefirst step in the activation of the nucleosides (Nu) consists of amonophosphorylation, leading to the corresponding monophosphate (NUMP).It is this first step which is the most selective.

In order to circumvent this key step of enzymatic monophosphorylation,it has already been proposed to adminster NuMPs directly, but their usefor therapeutic purposes was contraried by the abovementionedlimitations and drawbacks.

Compounds bearing a phosphate or phosphonate group have a negativelycharged ionic nature at physiological pH. The therapeutic activity ofsuch compounds is consequently limited, on account of the low diffusionof negatively charged compounds across biological lipid membranes. Inparticular, charged compounds do not diffuse efficiently across cellmembranes, or indeed across the cerebral barrier, which are lipidic innature. Moreover, such compounds are readily dephosphorylated by theaction of phosphatase enzymes in the blood or on the cell membranes,which enzymes dephosphorylate the substrate compounds thereof. Ingeneral, charged phosphate or phosphonate compounds are poorly absorbedvia oral administration.

It has been sought to convert mononucleotides into neutralphosphotriesters capable of crossing the cell membrane and ofintracellular delivery of the corresponding mononucleotidephosphotriester (NUMP). Such an approach has been adopted by variousauthors for a number of years, but has proved to be disappointing. Thederivatives obtained were in general either excessively toxic or ofinsufficient extracellular stability, and did not in the end resultprovide any enhancement of the biological activity.

Thus, the use of phosphorylated nucleoside structures comprisingbioreversible protecting groups of acyloxymethyl or acyloxybenzyl typehas been proposed, for antitumor nucleoside derivatives such as5-fluorouracil, in WO patents No. 9,008,155 and 9,119,721. However,these compounds are of limited chemical stability, and generate toxicformaldehyde metabolites in vivo. Furthermore, they are sparinglysoluble and the yield of their chemical preparation is low.

The aim of the present invention is thus to provide other types ofbioreversible groups which may be combined especially withmononucleotide or other structures such that the biological activitythereof is enhanced, in particular as regards compounds derived from oranalogous to nucleosides having antiviral activity, and which reversiblegroups do not have the abovementioned drawbacks.

The present invention proposes to use novel groups, characterized by thepresence of --SIS-- and/or --S/C═Z enzyme-labile bonds which lead, afterenzymatic activation, to the formation of unstable intermediates thatselectively release the corresponding monophosphate or monophosphonate.

More precisely, the subject of the present invention is the compoundcorresponding to the general formula I:

    RO--P(═O)(OR)--Nu                                      (I)

in which:

R is a radical --(CH₂)n-S--X, where X represents a radical --C(═Z)(Y) or--S--U, and Z is O or S;

Y and U represent an alkyl, aryl or saccharide radical which isoptionally substituted, in particular with an OH, SH or NH group; and

n is equal to 1 to 4, preferably 1 or 2;

Nu is a radical consisting of a residue of a biologically activecompound or the dephosphorylated residue of a compound which isbiologically active when it bears a phosphate or phosphonate group.

Moreover, the present invention also relates to the compoundcorresponding to the general formula Ia:

    RS--P(═O)(QR)--Nu                                      (Ia)

in which:

R is a radical --(CH₂)n-W--X, where X represents a radical --C(═Z)(Y) or--S--U, and Z is O or S;

Q is O or S;

W is O or S;

Y and U represent an alkyl, aryl or saccharide radical which isoptionally substituted, in particular with an OH, SH or NH group;

n is equal to 1 to 4, preferably 1 or 2; and

Nu is a radical consisting of a residue of a biologically activecompound or the dephosphorylated residue of a compound which isbiologically active when it bears a phosphate or phosphonate group.

When, in the formulas (I) and (Ia), Nu is linked to the phosphorus by aP--O bond, the compound of formulas (I) and (Ia) according to theinvention bears a phosphate group and thus constitutes a phosphotriestercompound.

When Nu is linked to the phosphorus by a P--C bond, the compound offormulas (I) and (Ia) according to the invention bears a phosphonategroup.

The mechanisms of bioreversibility of the radicals R take place viaenzymatic cleavage of the S--X or O--X bonds and release of the (CH₂)₂--S residues, according to the mechanisms which are illustrated by theexamples represented FIG. 1 and FIG. 9.

For Y and U there are especially mentioned, as alkyl group, a C₁ to C₇alkyl; as aryl group, phenyl and benzyl radicals, and, as saccharideradicals, glucose, mannose or rhamnose.

In one embodiment, when X represents SU, U preferably represents theradical --(CH₂)_(n1) --X¹ where X¹ represents H, OH, SH or NH₂ and n¹ isequal to 1 to 4, preferably 1 or 2.

There are especially mentioned the compounds (I) and (Ia) in which Rrepresents --(CH₂)₂ --S--S--(CH₂)₂ --OH.

In another embodiment, when X represents --C(═Z)Y, Y appropriatelyrepresents CH₃ or tBu.

There are especially mentioned the compounds (I) and (Ia) for which Rrepresents --(CH₂)_(n) --S--C(═O)--CH₃ or (CH₂)_(n) --S--C(═O)-tBu withn=1 or 2.

In an advantageous embodiment of the present invention, for thecompounds (I) and (Ia), there are especially mentioned the compounds forwhich Nu represents a 5' residue of a natural nucleoside or of aderivative of a natural nucleoside, which is therapeutically active orfor which the 5'-(O)-monophosphate or 5'-(C)-monophosphonate istherapeutically active.

These compounds of formulas (I) and (Ia) generally have antiviral orantitumor activity.

The compounds of formulas (I) and (Ia) for which Nu represents a 5'residue of 2',3'-dideoxynucleoside or 2',3'-didehydronucleoside are moreparticularly mentioned.

The compounds (I) and (Ia) for which Nu is a 5' residue of ddU(dideoxyuridine), ddT (dideoxythymidine), ddC (dideoxycytidine), AZT(3'-azido-2',3'-dideoxythymidine) and the derivatives thereof,especially those substituted on the pyrimidine base or at 2' and 3' ofthe saccharide ring, are more particularly mentioned among the compounds(I) and (Ia) derived from dideoxynucleosides having antiviral activity.

ddT, ddC or AZT are illustrations of the radicals Nu which represent a5' residue of a therapeutically active natural nucleoside derivative.

ddU is an illustration of the radicals Nu which represent a 5' residueof a nucleoside derivative which is only active in phosphorylated form.ddU (dideoxyuridine) is not enzymatically monophosphorylated in vivo.Only the triphosphate thereof is a polymerase inhibitor and impartsantiviral activity thereto.

The compounds for which Nu represents a 5' residue of the derivatives5'-fluorouridine or 5'-fluoro-2'-deoxyuridine or1-β-D-arabinofuranosylcytosine are especially mentioned among thecompounds (I) and (Ia) having antitumor activity. These compoundsillustrate the advantage of the functionalization according to theinvention in order to circumvent the resistance acquired to certainnucleoside drugs when this resistance is due to a loss of their abilityto be monophosphorylated, as is often the case in antitumorchemotherapy.

According to another embodiment variant of the invention, in thecompounds (I) and (Ia) the radical Nu represents a nucleoside analogresidue such as a carbonucleoside (nucleoside in which the oxygen of thesaccharide ring is replaced by a carbon), a phosphononucleoside(nucleoside in which the oxygen at 5' is replaced by a carbon) or apurine- or pyrimidine-based derivative of acyclonucleoside type, that isto say one which contains no saccharide ring, such as ACV (aciclovir),or a methoxyalkylpurine or pyrimidine radical of formula CH₂--O-alkylpurine or -pyrimidine.

The compounds (I) and (Ia) for which Nu represents a methoxyalkylpurineor -pyrimidine radical are illustrations of the phosphonate compounds.In the particular case of phosphonylmethoxyalkylpurine or -pyrimidineantiviral compounds, PMEA, HPMPA or HPMPC are especially mentioned, theformulae of which are given in FIGS. 3 and 4.

Thus, the present invention relates in particular to compounds in whichNu is a 3-hydroxy-2-methoxypropylpurine or -pyrimidine radical offormula: --CH₂ --OCH(CH₂ OH)--CH₂ -purine or -pyrimidine or a2-methoxyethylpurine or -pyrimidine radical of formula --CH₂ --O--C₂ H₄-pyrimidine and, for example, the compounds (I) and (Ia) for which Nu isa methoxyethyladenine or 3-hydroxy-2-methoxypropylcytosine radical.

When Nu represents a dephosphonylated residue (dephosphated ordephosphonated) of a molecule which is biologically active when it is inphospate or phosphonate form, the functionalization according to theinvention may enable the physicochemical and biophysical parameters ofthe said molecule comprising a phosphate or phosphonate group to bemodified in general. Compounds (I) and (Ia) may then consist, forexample, of a phosphopeptide or phospholipid compound.

When Nu represents a residue of a nucleoside, of a nucleoside derivativeor of a nucleoside analog, the latter may be D or L enantiomers.

The compounds according to the invention may be prepared by processesknown to those skilled in the art.

In particular, the subject of the present invention is a process for thepreparation of the compounds according to the invention, characterizedin that a compound of formulas (I) and (Ia) is prepared, in whichcompound the functional groups of R, and possibly of Nu, are protectedby suitable protecting groups, followed by deprotection of the saidfunctional groups of R, and possibly of Nu, in order to obtain thecompounds of formula (I) and (Ia).

In particular, a compound of formula (II):

    O.sup.- --P(═O)(O.sup.-)--Nu                           (II)

where Nu is possibly protected, is reacted in an appropriate manner withthe compound of formula (III):

    X--S--(CH.sub.2).sub.n --OH                                (III)

where X is protected, in order to obtain the said protected compound offormula (I), which is then deprotected.

In a particular embodiment, the reaction between the compounds offormula (II) and (III) takes place in the presence of a condensing agentsuch as MSNT, in pyridine.

Other preparation processes are illustrated in the examples whichfollow, in which other characteristics and advantages of the presentinvention will also appear.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous objects and advantages of the present invention may bebetter understood by those skilled in the art by reference to theaccompanying figures, in which:

FIG. 1 represents decomposition mechanisms for groups which arebioreversible under enzymatic activation. The same mechanism takes placefor both groups R.

FIG. 2 represents the decomposition mechanism for the bioreversiblegroup of the compound of Example 2.

FIG. 3 represents the formula of certain compounds according to theinvention.

FIG. 4 represents a preparation scheme for compounds prepared in Example1, and the formula of the compounds HPMPA and HPMPC.

FIG. 5 represents the preparation schemes for compounds prepared inExamples 2 and 3.

FIG. 6 represents the preparation scheme for compounds prepared inExample 4.

FIG. 7 represents the preparation scheme for compounds prepared inExamples 6-14.

FIG. 8 represents the preparation scheme for compounds prepared inExamples 15 and 16.

FIG. 9 represents the decomposition mechanism for the bioreversiblegroup of the compound of Example 16A.

FIG. 10 illustrates anti HIV activity in cell cultures comparingcompounds of Example 16A and 16B with similiar compounds of formula I.

DETAILED DESCRIPTION OF THE INVENTION

The advantage of this invention resides in the difference in stabilityof the mononucleotide phosphotriesters between extracellular andintracellular media; it is initially shown that the decomposition of oneof the compounds described in the invention (Example 2) complies fullywith the abovementioned criteria and occurs according to the mechanismshown FIG. 2.

The "ISRP on line" HPLC technique ("On-line Internal SurfaceReversed-Phase Cleaning: The Direct HPLC Analysis of Crude BiologicalSamples", A. Pompon, I. Lefebvre and J. L. Imbach, BiochemicalPharmacology, 43,1769-1775 (1992) was used for this study, the compoundstudied being incubated respectively in culture medium (RPMI/10%inactivated serum) and in a total cell extract (CEM).

The compound of Example 2 has a half-life of 9 hours in culture mediumand of less than 5 minutes in cell extract. The correspondingintracellular release of NUMP is corroborated by the demonstration ofbiological activity, whereas the constituent nucleoside is inactive.

Furthermore, insofar as the rate-determining step for activation of thephosphotriester into mononucleotide is highly dependent on the initialkinetics of enzyme hydrolysis, a variation in the nature of theenzymelabile groups leads to a modulation of the pharmacokineticparameters of the drug and results in delayactions.

These data clearly confirm the advantage of the invention.

Thin layer chromatographies were performed on Merck 60F 254 silicaplates (Art. 5554). Column chromatographies on silica gel were carriedout with Merck 60H silica (Art. 7736) or with RP2 Merck silanized silica(Art. 7719). Before analysis or lyophilization, the solutions werefiltered on Millex HV-4 filter (Millipore).

The UV spectra were recorded on a UVIKON 810 spectrophotometer.

Mass spectra were taken on a JEOL JMS DX 300 apparatus by the FABionization method in positive or negative mode in a matrix of glycerol(GT), glycerol/thioglycerol (GT) or 3-nitrobenzyl alcohol (NBA).

Proton NMR spectra were recorded on a Varian EM 360 apparatus or on aBruker AC 250 apparatus. The chemical shifts are expressed in ppmrelative to the tetramethylsilane (TMS) signal. The multiplicity and theappearance of the signals observed by NMR are indicated by one (or more)letter(s): s (singlet), d (doublet), t (triplet), m (multiplet), b(broad). Phosphorus NMR spectra were recorded on a Bruker WP 200 SYapparatus with proton decoupling. The chemical shifts are expressed inppm relative to the H₃ PO₄ signal which is taken as external reference.

EXAMPLE 1O-(2',3'-dideoxyuridin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl)phosphate(1)

(Scheme in FIG. 4)

2-Hydroxyethyl acetyl sulfide (5)

A solution of 1.0 ml (14 mmol) of thioacetic acid in 5 ml of toluene istreated with 0.90 ml (12 mmol) of iodoethanol in the presence of 1.7 ml(12 mmol) of 1,8-diazabicyclo-(5.4.0)-7-undecene (DBU) for 2 hours. Thereaction medium is diluted with dichloromethane and washed with water.The organic phase is dried over sodium sulfate and evaporated. The crudeproduct obtained is purified on a column of silica gel (eluent: methanol(0-4%) in dichloromethane) to give 1.2 g (85%) of 5 in the form of anoil.

5: ¹ H NMR (DMSO-d₆): d=2.32 (s, 3H, CH₃); 2.91 (t, 2H, CH₂ S, J=6.6Hz); 3.45 (pseudo q, 2H, CH₂ OH, J=6 Hz); 4.97 (t, 1H, OH) ppm.

O-(2',3'-dideoxyuridin-5'-yl) hydrogenophosphonate (6)

A 1.5M solution of phosphorous acid (165 ml, 247 mmol) in anhydrouspyridine is added to 5.25 g of 2',3'-dideoxy-uridine (24.7 mmol) and istreated with 16.8 ml of pivaloyl chloride (136 mmol). After reaction for3 hours, aqueous 1M triethylammonium bicarbonate solution is added toneutralize the mixture and the solvent is evaporated off under reducedpressure. The oil obtained is chromatographed on a column of silica gel(eluent: methanol (0-35%) in dichloromethane) to give 6. The product istaken up in methanol and is filtered on a Millipore filter. Evaporationof the solvent gives 7.10 g (76%) of 6 (in triethylammonium form) whichis sufficiently pure for use in the next step of the synthesis. A sampleof higher purity is obtained after an additional purification by thinlayer chromatography on silica gel, using a mixture of isopropanol,ammonia solution and water (8:1:1) as eluent. The product, in ammoniumform, is extracted from the silica with methanol, the solvent isstripped off by evaporation and the residue is taken up in water,filtered on a Millipore filter and lyophilized.

6: LTV (H₂ O): Λ_(max) =262 nm (e 9940); Λ_(min) =230 nm (e 2080)

MS (negative FAB, GT); 275 (M)⁻

¹ H NMR (DMSO-d₆); d=1.78-2.05 (m: 3H, H-2',3',3"2.18-2.45 (m, IH,H-2"); 3.65-3.95 (m, 2H, H-5',5"); 4.11 (m, 1H, H-4"); 5.55 (d, 1H, H-5,J=8.1 Hz); 5.95 (dd, 1H, H-1',J=6.8 and 3.8 Hz); 6.63 (d, 1E, HP, J=592Hz); 7.87 (d, 1H, H-6, J=8.1 Hz) ppm 31 P NMR (DMSO-d₆): d=1.60 ppm.

O-(2',3'-dideoxyuridin-5'-yl)-O,O'-bio(S-acetyl-2-thioethyl)phosphate(1)

A solution of 200 mg (0.530 mmol) of the hydrogenophosphonate 6 of2',3'-dideoxyuridine in 5 ml of pyridine is treated with 196 μl ofpivaloyl chloride for 30 minutes. 159 mg (1.33 mmol) of 2-hydroxyethylacetyl sulfide (5) are added and the reaction is left stirring for 2hours. The phosphate formed is oxidized using 2% a iodine solution in apyridine-water mixture (98:2) until a persistent coloration is obtained(7-8 ml). The solvent is evaporated off under reduced pressure. Thecrude product obtained is co-evaporated with toluene and chromatographedon a column of silica gel (eluent: methanol (0-6%) in dichloromethane)to give 65 mg (25%) of compound 1 in the form of an oil.

1: UV (EtOH): Λ_(max) =262 nm (e 9400); Λ_(min) =230 nm (e 2500)

MS (positive FA.B): 497 (M+H)⁺

¹ H NMR (DMSO-d₆): d=1.73-2.13 (m, 3H, H-2',3',3") 2.20-2.4 (m, 1H,H-2"); 2.356 and 2.360 (s and s, 3H and 3H. 2 CH₃); 3.13 (t, 4H, 2 CH₂S, J=6.4 Hz); 4.00-4.26 (m, 7H, H-4',5',5" and 2 CH₂ CH₂ OP); 5.60 (d,1H, H-5, J=8.1 Hz); 6.01 (dd, 1H, H-1', J=4.2 and 7.0 Hz); 7.64 (d, 1H,H-6, J=8.1 Hz); 11.3 (bs, 1H, NHCO) ppm.

³¹ P NMR (DMSO-d₆): d=-1.21 ppm

EXAMPLE 2O,O'-Bis(S-(2-hydroxyethylsulfidyl)-2-thioethyl)-o-(2',3'-dideoxyuridin-5'-yl)phosphate (2).

(Scheme in FIG. 5)

O,O'-Bis (S-(O-(4-methoxytrityl)-2-oxethylsufidyl)-2-thioethyl)phosphate(8).

To a solution of 0.910 g (13.4 mmol) of imidazole in 18 ml of pyridineat 0 C. is added 0.406 ml (4.45 mmol) of phosphorus oxychloride. Themixture is stirred for 30 minutes at room temperature, then added to3.80 g (8.91 mmol) of mono-O-(4-methoxytrityl)dithiodiethanol (7). After18 hours, the reaction mixture is treated with 1M triethylammoniumacetate solution. The reaction products are extracted withdichloromethane and the organic phase is washed with water, dried oversodium sulfate, concentrated under reduced pressure and co-evaporatedwith toluene. Purification on a column of silica gel (eluent: methanol(0-10%) in dichloromethane) gives 2.2 g (48%) of 8 in the form of thetriethyl-ammonium salt.

8: MS (negative FAB, NBA): 913 (M⁻).

¹ H NMR (DMSO-d₆) 1.14 (t, 9H, (CH₃ CH₂) ₃ NH 1 J=7.3 Hz); 2.78 (t, 4H,2 SCH₂ CH₂ OP, J=6.4 Hz); 2.86 (t, 4H, 2 SCH₂ CH₂ OMTr, J=6 Hz);2.99 (q,6H, (CH₃ CH₂) ₃ NH⁺, J=7.3 Hz); 3.21 (t, 4H, 2 CH₂ OMTr, J=5.9 Hz); 3.71(s, 6H, 2 CH₃ O); 3.87 (m, 4H, 2 CH₂ OP); 6.82-7.45 (m, 28H, 2 Tr) ppm.

³¹ P NMR (DMSO-d₆): -2.70 ppm.

O,O'-Bis(S-(2-hydroxyethylsufidyl)-2-thioethyl)-O-(2',3'-dideoxyuridin-5'-yl)phosphate(2).

A mixture of 666 mg (0.655 mmol) of 8 and 139 mg (0.656 mmol) of2',3'-dideoxyuridine in 5 ml of pyridine is treated with 486 mg (1.64nmol) of 1-(2-mesitylene-sulfonyl)-3-nitro-1,2,4-triazole. After 30hours, the reaction mixture is diluted with dichloromethane and washedwith aqueous 1M triethylammonium acetate solution and then with water.The organic phase is dried over sodium sulfate, concentrated underreduced pressure, coevaporated with toluene and chromatographed on acolumn of silica gel (eluent: methanol (0-4%) in dichloromethane). Thepartially purified protected phosphotriester is treated with 5 ml of theacetic acid/water/methanol mixture (8:1:1) for 24 hours. The solventsare stripped off by evaporation under reduced pressure and the oilobtained is co-evaporated with toluene. Purification on a column ofsilica gel (eluent: methanol (0-6%) in dichloromethane) followed bypurification on a column of silanized silica (eluent: ethanol (0-40%) inwater) gives 52 mg (14%) of compound 2 after lyophilization in dioxane.

2: LTV (EtOH): Λ_(max) 261 nm (ε9900); Λ_(min) 231 nm (ε3100)

MS (positive FA.B, GT): 565 (M+H)⁺ : 489 (M--SCH₂ CH₂ OH+2H)⁺ ; 429(M--HOCH₂ CH₂ SSCH₂ CH₂ +2H)⁺.

¹ H NMR (DMSO-d₆): 1.63-1.9 (m, 1H, H-3'); 1.9-2.10 (m, 2H, H-2'3");2.33-2.40 (m, 1H, H-2"); 2.80 (t, 2H,HOCH₂ CH₂ S, J=6.4 Hz); 2.81 (t,2H, HOCH₂ CH₂ S, J=6.4 Hz); 3.00 (t, 4H, 2 SCH₂ CH₂ OP, J=6.3 Hz); 3.61(pseudo q, 4H, 2, HOCH₂, J=6 Hz), 4.07-4.32 (m, 7H, H-4', 5', 5" and 2CH₂ CH₂ OP); 4.89 (t, 2H, 2 HO, J=4.9 Hz); 5.598 (d, 1H, H-5, J=8.1 Hz);5.604 (d, 1H, H-5, J=8.1 Hz); 6.00 (dd, 2H, 2H-1', J=4.1 and 7.9 Hz);7.65 (d, 2H, 2 H-6, J=8.0 Hz); 11.31 (bs, 1H, NHCO)ppm.

³¹ P NMR (DMSO-d₆): -0.880 ppm

EXAMPLE 3O,O'-Bis(S-(2-hydroxyethylsufidyl)-2-thioethyl)-O-(3'azido-3'-deoxythymidin-5'-yl)phosphate(3).

(Scheme in FIG. 5)

A mixture of 666 mg (0.655 mmol) of 8 and 193 mg (0.722 mmol) of3'-azido-3'-deoxythymidine in 5 ml of pyridine is treated with 486 mg(1.64 mmol) of 1-(2-mesitylenesulfonyl)-3-nitro-1,2,4-triazole. After 24hours, 194 mg (0.656 mmol) of1-(2-mesitylenesulfonyl)-3-nitro-1,2,4-triazole are added and thereaction is left for a further 24 hours. The reaction mixture is thendiluted with dichloromethane and washed with aqueous 1M triethylammoniumacetate solution and then with water. The organic phase is dried oversodium sulfate, concentrated under reduced pressure, co-evaporated withtoluene and chromatographed on a column of silica gel (eluent: methanol(O-2%) in dichloromethane). The partially purified protectedphosphotriester is treated with 5 ml of the acetic acid/water/methanolmixture (8:1:1) for 24 hours. The solvents are stripped off byevaporation under reduced pressure and the oil obtained is co-evaporatedwith toluene. Purification on a column of silica gel (eluent: methanol(0-6%) in dichloromethane) gives 130 mg (29%) of compound 3 afterlyophilization in dioxane.

3: UV (EtOH): Λmax 264 nm (ε9600), Λ_(min) 234 nm (ε2100)

MS (positive FAB, GT): 620 (M+H)⁺ ; 544 (M--SCH₂ CH₂ OH+2H)⁼

1H NMR (DMSO-d₆): 1.80 (s, 3H, CH₃); 2.26-2.5 (m, 2H, H-2' 2"); 2.796(t, 2H, HOCH₂ CH₂ S, J=6.4 Hz); 2.802 (t, 2H, HOCH₂ CH₂ S, J=6.4 Hz);2.99 (t, 4H, 2 SCH₂ CH₂ OP, J=6.3 Hz); 3.61 (pseudo q, 4H, 2 HOCH₂ ' J=6Hz); 4.02 (m, 1H, H-4'); 4.09-4.44 (m, 6H, H-5',5" and 2 CH₂ CH₂ OP);4.48 (m, 1H, H-3'); 4.90 (t, 2H, 2 HO, J=5.3 Hz); 6.14 (t, 1H, H-1',J=6.6 Hz); 7.49 (s, 1H, H-6); 11.37 (bs, 1H, NHCO) ppm.

³¹ P NMR (DMSO-d₆): -0.954 ppm

EXAMPLE 49-(2-(O,O'-Bis(S-(2-hydroxyethylsufidyl)-2-thioethyl)phosphonylmethoxy-ethyl)adenine(4)

(Scheme in FIG. 5)

N6-(4-Methoxytrityl)-9-(2-diethoxyphosphonylmethoxy ethyl)adenine (10).

A solution of 3.93 g (11.9 mmol) of9-(diethoxyphosphonylmethoxyethyl)adenine (9) (A. Holy et al.,Collection Czechoslovak Chem. Commun. 52 2792, 1987) and 146 mg (1.19mmol) of 4-dimethylaminopyridine in 50 ml of dichloromethane is treatedwith 3.31 ml (23.8 mmol) of triethylamine and 7.35 g (23.8 mmol) of4-methoxytrityl chloride for 4 hours. The reaction mixture is thendiluted with dichloromethane and washed with aqueous sodium hydrogencarbonate solution and then with water.

The organic phase is dried over sodium sulfate and concentrated underreduced pressure. Chromatography on a column of silica gel (eluent:methanol (0-3%) in dichloromethane) allows 5.43 g (84%) of compound 10to be isolated.

10: UV (EtOH): Λ_(max) 275 nm (ε27200), Λ_(min) 246 nm (ε11200)

MS (negative FAB, GT) 601 (M-H)⁻ ; 406 (A^(mTr))⁻ ; 328 (M--MTr)--

¹ H NMR (DMSO-d₆): 1.10 (t, 6H, 2 CH₃ CH₂, J=7.0 Hz); 3.71 (s, 3H, CH₃O), 3.80-3.98 (m, 4H. PCH₂ and CH₂ CH₂); 3.88 (q, 4H, 2 CH₃ CH2' J=8Hz); 4.33 (t, CH₂ CH₂ ' J=4.8 Hz); 6.80-7.37 (m, 14H, Tr); 7.91 (s, IH,H-8); 8.18 (s,H-2) ppm.

³¹ P NMR (DMSO-d₆): 21.35 ppm.

N⁶ -(4-Methoxytrityl)-9-(2-phosphonylmethoxyethyl)adenine (11).

A solution of 5.00 g (8.31 mmol) of 10 in 29 ml of acetonitrile istreated with 3.29 ml (24.9 mmol) of trimethylsilyl bromide for 14 hours.The excess reagent and the solvent are stripped off by evaporation underreduced pressure. The oil obtained is taken up in triethylanmoniumbicarbonate and concentrated under reduced pressure. Purification isperformed by chromatography on a column of silica gel (eluent: methanol(0-50% ) in dichloromethane). After filtration in solution indi-chloromethane, 3.4 g (63%) of 11 are isolated in the form of a mixedsalt of acid and triethylanmonium (1:1).

11: MS (negative FAB, GT): 544 (M-H)⁻ : 272 (M--MTr)⁻.

¹ H NMR (DMSO-d₆): 1.11 (t, 9H, (CH₃ CH₂)NH⁺, J=7.3 Hz); 2.96 (q, 6H,(CH₃ CH₂)NH⁺, J=7.3 Hz); 3.34 (d, 2H, PCH₂, J=8.4 Hz); 3.68 (s, 3H, CH₃O); 3.8 (m, 2H, CH₂ CH₂); 4.27 (t, CH₂ CH₂, J=4.5 Hz); 6.65-7.35 (m,14H, Tr); 7.83 (s, 1H, H-8); 8.31 (s, 1H, H-2) ppm.

³¹ P NMR (DMSO-d₆): 11.40 ppm.

N⁶ -(4-Methoxytrityl)-9-(2-O,O-bio(S-(O-(4-methoxytrityl)-2-oxethylaufidyl)-2-thioethyl))phosphonylmethoxyethyl)adenine(12).

A mixture of 296 mg (0.458 mmol) of 11 with 977 mg (2.29 nmol) ofmono-O-(4-methoxytrityl) dithiodiethanol (7) in 5 ml of pyridine istreated with 341 mg (1.15 mmol) of1-(2-mesitylenesulfonyl)-3-nitro-1,2,4-triazole. After 3 days, thereaction mixture is diluted with dichloromethane and washed withsaturated aqueous sodium hydrogen carbonate solution and then withwater. The organic phase is dried over sodium sulfate, concentratedunder reduced pressure, co-evaporated with toluene and chromatographedon a column of silica gel (eluent: methanol (0-5%) in dichloromethane)to give 330 mg (53%) of 12.

12: UV (EtOH): Λ_(max) 275 nm (ε28200), Λ_(min) 253 nm (ε18300)

MS (negative FAB, NBA) 1360 (M-H)-: 952 (M--MtrOCH₂ CH₂ SSCH₂ CH₂)--.

¹ H NMR (DMSO-d₆): 2.75 (t, 4H, 2 SCH₂ CH₂ OP, J=6.3 Hz) 2.86 (t, 4H, 2CH₂ CH₂ OMTr, J=5.9 Hz); 3.19 (t, 4H, 2 CH₂ OMTr, J=6.0 Hz); 3.68 (s,3H, CH₃ O); 3.69 (s, 6H, 2 CH₃ O); 3.83 (m, 4H, PCH₂ and CH₂ CH₂); 4.05(m, 4H, 2 CH₂ OP); 4.28 (t, 2H, CH₂ CH₂, J=4.6 Hz); 6.87-7.45 (m, 42H, 3Tr); 7.88 (s, 1H, H-8); 8.12 (s, 1H, H-2)ppm.

³¹ P NMR (DMSO-d₆): 22.09 ppm.

9-(2-(O,O'-Bis(S-(2-hydroxyethylsufidyl)-2-thioethyl)phosphonylmethoxyethyl)adenine(4).

The phosphotriester 12 (290 mg, 0.213 mmol) is treated with 15 ml of theacetic acid/water/methanol mixture (8:1:1) for 15 hours. The solventsare stripped off by evaporation under reduced pressure and the oilobtained is co-evaporated with toluene. Purification on a column ofsilica gel (eluent: methanol (0-8%) in dichloromethane) gives 116 mg(90%) of compound 4 after lyophilization in the water/dioxane mixture.

4: LTV (EtOH): Λ_(max) 260 nm (ε14700); Λ_(min) 228 nm (ε3600).

MS (positive FAB, GT): 545 (M+H)⁺

¹ H NMR (DMSO-d6): 2.80 (t, 4H, 2 SCH₂ CH₂ OP, J=6.4 Hz); 2.91 (t, 4H, 2SCH₂ CH₂ OH, J=6.4 Hz); 3.61 (pseudo q, 4H, 2 CH₂ OH, J=6 Hz); 3.91 (t,2H, CH₂ CH₂, J=5.1 Hz) 3.95 (d, 2H, PCH₂,J=8.2 Hz); 4.15 (m, 4H, 2 CH₂OP); 4.32 (t, 2H, CH₂ CH₂, J=5.0 Hz); 7.20 (bs, 2H, NH₂); 8.08 (s, 1H,H-8); 8.14 (s, 1H, H-2) ppm.

³¹ P NMR (DMSO-d₆): 22.24 ppm.

EXAMPLE 5 EVALUATION OF THE ANTI-HIV I ACTIVITY ON CEM CELLS AND MT-4CELLS

HIV=Human immunodeficiency virus

MT-4=Human leukemia T cell

CEM=Human lymphoblastoid T cell

HIV-1 replication (LAI isolate) in CEM cells is measured by assaying thereverse transcriptase (RTase) in the culture supernatant after infectionfor 5 days. This activity reflects the presence of the virus released bythe cells. After adsorption of the virus, the test compounds are added,at various concentrations, to the culture medium.

Antiviral activity is expressed as the lowest concentration of compoundwhich reduces the production of RTase by at least 50% (ED₅₀).

The toxic effect on non-infected CEMs is assessed by a calorimetricreaction based on the capacity of living cells to reduce3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide intoformazan after incubation for 5 days in the presence of variousconcentrations of the compounds. The results are expressed as the lowestconcentration of compound which results in at least 50% inhibition ofthe formation of formazan (CD₅₀).

The compounds used as examples in this invention have the followinganti-HIV activities:

    ______________________________________                                        Compound 1:                                                                   ED.sub.50                                                                              CEM-TK-,    4.10.sup.-6 M                                                                            (CD.sub.50 7.10.sup.-5 M)                              CEM-SS,     5.10.sup.-6 M                                                                            (CD.sub.50 9.10.sup.-5 M)                              MT4,        2.10.sup.-6                                                                              (CD.sub.50 9.10.sup.-5 M)                     Compound 2:                                                                   ED       CEM-TK-,    8.10.sup.-6 M                                                                            (CD.sub.50 8.10-5 M)                                   CEM-SS,     6.10.sup.-5 M                                                                            (CD.sub.50 10.sup.-4 M)                       Compound 3                                                                    ED.sub.50                                                                              CEM-TK-,    7.10.sup.-6 M                                                                            (CD.sub.50 8.10.sup.-5 M)                              CEM-SS,     7.10.sup.-10 M                                                                           (CD.sub.50 8.10.sup.-5 M)                              MT4         10.sup.-9 M                                                                              (CD.sub.50 8.10.sup.-5 M)                     Compound 4:                                                                   ED.sub.50                                                                              CEM-TK-,    8.10-8 M   (CD.sub.50 4.10.sup.-5 M)                              CEM-SS,     3.10-6 M   (CD.sub.50 >10.sup.-4 M)                               MT4,        8.10-7 M   (CD.sub.50 2.10.sup.-5 M)                     ______________________________________                                    

This set of data shows that there has indeed been intracellular releaseof the nucleoside monophosphate.

EXAMPLE 6 O,O'-Bis(S-acetyl-2-thioethyl)-N,N-diisopropylphosphoramidite

To a stirred solution of N,N-diisopropylphosphorodichloridate (4.04 g,20 mmol) in tetrahydrofuran (150 ml) at -78° C. was added dropwise over45 minutes a solution of S-acetylthioethanol (4.81 g, 40 mmol) andtriethylamine (5.53, 40 mmol) in tetrahydrofuran (100 ml). The resultingreaction mixture was stirred for 2 hours at ambient temperature thenfiltered. The filtrate was concentrated under vacuum and the residue wasdiluted with cyclohexane and filtered. The filtrate was concentrated toa residue under vacuum, Diluted with cyclohexane, filtered andconcentrate again. The final residue was chromatographed on a silica gelcolumn. The column was eluted with a gradient of ethyl acetate incyclohexane (0→20%) containing 5% triethylamine to obtain the titlecompound, O,O'-bis(S-acetyl-2-thioethyl-N,N-diisopropylphosphoramidite(5.3 g, 72%).

Mass Spec (FAB positive, GT): 370 (M+H)⁺, 103 CH₃ C(O)SCH₂ CH₂ !⁺.

NMR ⁻ H (DMSO-d₆): 3.70-3.47 (m, 6H, 2 CH₂ OP, 2 CH(CH₃)₂); 3.04 (t, 4H,2SCH₂ CH₂ J=6.4 Hz); 2.32 (s, 6H, 2CH₃ COS); 1.10 (d, 12H, 2 CH(CH₃)₂),J=6.8 Hz) ppm. NMR ³¹ P (DMSO-d₆): 147.9 ppm (q).

EXAMPLE 7 General procedure forO-(2',3'-dideoxynucleosid-5'-yl)-O'-O"-bis(S-acetyl-2-thioethyl)phosphates

To a solution of a 2',3'-dideoxynucleoside AZT (0.1 g, 0.37 mmol); ddA(0.05 g, 0.5 mmol); ddI (0.12 g, 0.5 mmol); or ddT (0.11 g, 0.5 mmol)!and O,O'-bis(S-acetyl-2-thioethyl)-N,N'-diisopropylphosphoramidite (1.2eq.) in a mixture of tetrahydofuran/dimethylforamide (1:1, v/v, 5 ml permmol) was added sublimed tetrazole (3.0 eq). After 30 min of stirring atambient temperature the reaction mixture was cooled to -40° C. and asuspension of 3-chloroperbenzoic acid (1.3 eq) in dichloromethane (2 mlper mmol) was added. After stirring for one hour at ambient temperaturethe excess peracid was reduced with an aqueous solution of 10% sodiumthiosulfate. The crude residue was diluted with dichloromethane andextracted with a saturated aqueous solution of sodium bicarbonate. Theorganic phase was wash with water, dried over sodium sulfate, filteredand evaporated under vacuum. The residue was chromatographed on a silicagel column eluted with a step gradient of methanol in dichloromethane togive the title bis(SATE)phosphotriesters as pure products.

EXAMPLE 8O-(2',3'-Dideoxy-3'-azidothymidin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl)phosphate

Bis (SATE)AZTMP!

Prepared as per the above general procedure to give 0.11 g (53%) of thetitle compound.

UV (EtOH): Λ_(max) 264 nm (ε9800), λ_(min) 246 nm (ε6500).

Mass Spec. (FAB positive, GT) 552 (M+H)⁺, (FAB negative, GT): 550(M-H)⁻.

NMR ¹ H (DMSO-d6): 11.36 (sl, 1H, NH-3); 7.46 (d, 1H, H-6, J_(H-6),CH3-5 =0.7 Hz); 6.13 (t, 1H, H-1', J_(H1'),2" =6.7 Hz) 4.46 (m, 1H,H-3'); 4.20 (m, 2H, H-5',5"); 4.03 (m, 5H, H-4', CH₂ --CH₂ --O), 3.12(t, 4H, S--C--H_(2a) --CH_(2b), J_(Ha),Hb =6.3 Hz); 2.42 (m, 8H,H-2',2", CH₃ --CO); 1.78 (s, 3H, CH₃ -5) ppm.

EXAMPLE 9O-(2',3'-Dideoxyadenosin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl)-phosphate

Bis(SATE)ddAMP!

Prepared as per the above general procedure to give 0.65 g (50%) of thetitle compound.

UV (EtOH): Λ_(max) 260 nm (ε12000), 229 nm (ε8600), λ_(min) 240 nm(ε7200), 223 nm (ε7900).

Mass Spec. (FAB positive, GT): 520 (M+H)⁺, 136 (BH₂)⁺ ; (FAB negative,GT): 416 (M--CH₃ C(O)SCH₂ CH₂)⁻, 134 (B)⁻.

NMR ¹ H (DMSO-d6): 8.25 & 8.13 (2s, 1H & 1H, H-2 & H-8); 7.24 (s, 2H,NH₂); 6.24 (t, 1H, J=5.4 Hz, H-1'); 4.28 (m, 1H, H-4'); 4.18-4.03 (m,2H, H-5'& H-5"); 3.96 (q, 4H, 2 S--CH₂ --CH₂ --O); 3.06 (t, 4H, J=6.3Hz, 2 S--CH₂ --CH₂ --O); 2.48 (m, 2H, H-2'& H-2"); 2.32 & 2.31 (2s, 3H &3H, 2 CH₃) ppm.

NMR ³¹ P (DMSO-d₆) 0.78 ppm.

EXAMPLE 10O-(2',3'-Dideoxyinosin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl)-phosphate

Bis(SATE)ddIMP!

Prepared as per the above general procedure to give 0.21 g (81%) of thetitle compound.

UV (EtOH) Λ_(max) 242 nm (ε14700), 235 nm (ε14900), shoulder 266 nm(ε5800) & 248 nm (ε13400).

Mass Spec. (FAB positive, GT): 521 (M+H)^(+b) , 137 (BH₂)⁺, 103 (CH₃C(O)SCH₂ CH₂)⁺ ; (FAB negative, GT) 519 (M-H)⁻, 135 (B)⁻.

NMR ¹ H (DMSO-d6): 12.36 (s, 1H, NH-1); 8.21 (s, 1H, H-2); 8.04 (s, 1H,H-8); 6.22 (m, 1H, H-1'); 4.28 (m, 1H, H-4'); 4.20-4.02 (m, 2H, H-5'&H-5"); 3.97 (m, 4H, 2 S--CH₂ --CH₂ --OP); 3.07 (t, 4H, J=6.4 Hz, 2S--CH₂ --CH₂); 2.49-2.42 (m, 2H, H-2' & H-2"; 2.33 (s, 3H, CH₃ COS),2.32 (s, 3H, CH₃ COS), 2.15-2.02 (m, 2H, H-3' & H-3") ppm.

NMR ³¹ P (DMSO-d6) 0.77 (m) ppm.

EXAMPLE 11O-(2',3'-Dideoxythymidin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl)-phosphate

Bis(SATE)ddTMP!

Prepared as per the above general procedure to give 0.23 g (91%) of thetitle compound.

UV (EtOH) λ_(max) 266 nm (ε8800), λ_(min) 246 nm (ε5400).

NMR ¹ H (DMSO-d6): 11.29 (s, 1H, NH-3); 7.47 (d, 1H, H-6; J=1.0 Hz);6.01 (m, 1H, H-1'), 4.20-4.11 (m, 3H, H-4',H-5',5"); 4.04 (m, 4H, 2 CH₂-CH₂ -OP); 3.11 (t, 4H, S--C--H_(2a) --CH_(2b), J=6.3 Hz); 2.34 (s, 3H,CH₃ --COS); 2.33 (s, 3H, CH₃ --COS); 2.33-2.25 (m, 1H, H-2"); 2.00-1.90(m, 3H, H-2",3',3"); 1.78 (d, 3H, CH₃ -5, J=0.6 Hz) ppm.

NMR ³¹ P (DMSO-d₆) 0.56 ppm.

EXAMPLE 12 N⁶-(4-Methoxytrityl)-9-(2-(O,O'-bis(S-acetyl-2-thioethyl)-phosphonylmethoxyethyl)adenine

Bis(SATE)PMEA-MTr!

To a solution of N⁶-(4-methoxytrityl)-9-(2-phosphonylmethoxyethyl)adenine (compound 11) asa mixture of triethylammonium salts (0.25:0.75, 0.3 g, 0.43 mmol),1-(2-mesitylenesulfonyl)-3-nitro-1,2,4-triazole (0.41 g, 1.38 mmol) inanhydrous pyridine (6 ml) was added S-acetylthioethanol (0.33 g, 2.77mmol). The reaction mixture was stirred overnight at ambient temperatureand then neutralized with an aqueous triethylammonium bicarbonate (1M,pH 7.5, 4 ml). Chloroform and water were added, the organic phase wasdecanted, dried over sodium sulfate, filtered and evaporated undervacuum. The residue was chromatographed on a silica gel column elutedwith a gradient methanol in dichloromethane (0→2%) to give the titlecompound, bis(SATE)PMEA-MTr (0.15 g, 50%), as an oil.

Mass Spec. (FAB positive, GT): 750 (M+H)⁻.

NMR ¹ H (DMSO-d6): 8.15 & 7.90 (2s, 1H & 1H, H-2 & H-8); 7.31-6.81 (m,15H, trityl & NH); 4.32 (t, 2H, J=4.7 Hz, CH₂ N); 3.99-3.84 (m, 8H, 2S--CH₂ --CH₂ --O, CH₂ --P, CH₂ CH₂ --N); 3.70 (s, 3H, OCH₃); 3.01 (t,4H, J=6.4 Hz, S--CH₂ --CH₂ --O); 2.30 (s, 6H, 2 CH₃) ppm.

NMR ³¹ P (DMSO-d₆) 22.51 ppm.

EXAMPLE 139-(2-(O,O'-Bis(S-acetyl-2-thioethyl)phosphonylmethoxyethyl)adenine

Bis (SATE) PMEA!

A solution of bis(SATE)PMEA^(MTr) (0.21 g, 0.28 mmol) in aceticacid:water:methanol (8:1:1, v/v/v, 22 ml) was stirred overnight atambient temperature. The reaction mixture was evaporated and the residueco-evaporated with 100% ethanol and dichloromethane. The residue waschromatographed on a silica gel column to give pure bis(SATE)PMEA (0.079g, 59%). m.p. 66° C. (crystallized from toluene).

UV (EtOH) λ_(max) 260 nm (ε14200), 230 nm (ε10400), λ_(min) 240 nm(ε9200), 223 nm (ε9800).

Mass Spec. (FAB positive, GT): 570 (M+G+H)⁺, 478 (M+H)⁺ ; (FAB negative,GT): 374 (M--CH₃ C(O)SCH₂ CH₂)⁻.

NMR ¹ H (DMSO-d6): 8.12 & 8.06 (2s, 1H & 1H, H-2 & H-8); 7.17 (s, 2H,NH₂); 4.31 (t, 2H, J=5.0 Hz, CH₂ N); 4.00--3.86 (m, 8H, 2 S--CH₂ --CH₂--O, CH₂ --P, CH₂ --CH₂ --N); 3.03 (t, 4H, J=6.4 Hz, 2 S--CH₂ --CH₂--O); 2.33 (s, 6H, 2 CH₃) ppm.

NMR ³¹ P (DMSO-d₆) 22.53 ppm.

EXAMPLE 14 EVALUATION OF THE ANTI-HIV 1 ACTIVITY ON CEM CELLS AND MT-4CELLS OF BIS(SATE)PHOSPHOTRIESTERS OF AZT, ddA, ddI, ddT AND PMEA

The compounds were tested as described in Example 5 above.

    ______________________________________                                        AZT                                                                           ED.sub.50                                                                              CEM-TK.sup.-                                                                             >10.sup.-4 M                                                                             (CD.sub.50 > 10.sup.-4 M)                               CEM-SS     4.8 10.sup.-9 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±2.4 10.sup.-9                                                  MT-4       1.8 10.sup.-8 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±0.6 10.sup.-8                                         Bis (SATE) AZTMP                                                              ED.sub.50                                                                              CEM-TK.sup.-                                                                             3.9 10.sup.-8 M                                                                          (CD.sub.50 ND)                                          CEM-SS     2.2 10.sup.-8 M                                                                          (CD.sub.50 ND)                                          MT-4       7.8 10.sup.-8 M                                                                          (CD.sub.50 7.6 10.sup.-5 M)                    ddA                                                                           ED.sub.50                                                                              CEM-TK.sup.-                                                                             1.1 10.sup.-6 M                                                                          (CD.sub.50 > 10.sup.-4 M)                               CEM-SS     5.4 10.sup.-7 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±1.1 10.sup.-7                                                  MT-4       10.sup.-5 M                                                                              (CD.sub.50 > 10.sup.-4 M)                      Bis (SATE) ddAMP                                                              ED.sub.50                                                                              CEM-TK.sup.-                                                                             7.7 10.sup.-10 M                                                                         (CD.sub.50 > 10.sup.-5 M)                               CEM-SS     5.6 10.sup.-10 M                                                                         (CD.sub.50 2.4 10.sup.-5 M)                                        ±3.4 10.sup.-10                                                                       ±0.1 10.sup.-5                                       MT-4       1.1 10.sup.-8 M                                                                          (CD.sub.50 1.6 10.sup.-5 M)                                        ±0.8 10.sup.-8                                                                        ±0.9 10.sup.-5                              ddI                                                                           ED.sub.50                                                                              CEM-TK.sup.-                                                                             9.5 10.sup.-7 M                                                                          (CD.sub.50 > 10.sup.-4 M)                               CEM-SS     4.3 10.sup.-6 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±2.0 10.sup.-6                                                  MT-4       1.1 10.sup.-5 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±0.2 10.sup.-5                                         Bis (SATE) ddIMP                                                              ED.sub.50                                                                              CEM-TK-    3.0 10.sup.-7 M                                                                          (CD.sub.50 > 10.sup.-4 M)                               CEM-SS     1.2 10.sup.-6 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±0.6 10.sup.-6                                                  MT-4       3.4 10.sup.-6 M                                                                          (CD.sub.50 > 10.sup.-4 M)                                          ±1.1 10.sup.-6                                         ddT                                                                           ED.sub.50                                                                              CEM-TK.sup.-                                                                             >10.sup.-4 M                                                                             (CD.sub.50 > 10.sup.-4 M)                               CEM-SS     4.0 10.sup.-6 M                                                                          (CD.sub.50 > 10.sup.-4 M)                               MT-4       ND         (CD.sub.50 ND)                                 Bis (SATE) ddTMP                                                              ED.sub.50                                                                              CEM-TK.sup.-                                                                             5 10.sup.-7 M                                                                            (CD.sub.50 > 10.sup.-4 M)                               CEM-SS     1.7 10.sup.-6 M                                                                          (CD.sub.50 8.5 10.sup.-5 M)                             MT-4       ND         (CD.sub.50 ND)                                 ______________________________________                                    

In the same manner as was seen for the activities exhibited in Example5, the anti HIV activity of the above listed bis(SATE) derivatives showincreases of up to 1/3log units compared to their parent nucleosides(compare AZTMP and ddTMP to the parent nucleosides AZT and ddT,respectively). This increase in activity shows that there wasintercellular release of the nucleoside monophosphate.

For Examples 15 and 16 below, ¹ H NMR were recorded using a Bruker AC250 or a Bruker AC 400 spectrometer at ambient temperature in CDCl₃.Chemical shifts are given in δ-values referenced to the residual solventpeak (7.26 ppm). Deuterium exchange, decoupling and COSY experimentswere performed in order to confirm proton assignments. ³¹ P NMR spectrawere recorded at ambient temperature on a Bruker AC 250 spectrometer at101.2 MHz with proton decoupling. Chemical shifts are reported relativeto external H₃ PO₄. ³¹ C NMR spectra were measured on a Bruker AC 400spectrometer at 100.6 MHz with proton decoupling using CDCl₃ (77.00 ppm)as internal standard. Coupling constants, J, are reported in hertz. FABmass spectra were reported in the positive-ion or negative-ion mode on aJEOL DX 300 mass spectrometer operating with a JMA-DA 5000 mass datasystem using thioglycerol/glycerol (1:1, v/v, G--T) as matrix. Xe atomswere used for the gun at 3 kV with a total discharge current of 20 mA.UV spectra were recorded on an Uvikon 810 (Kontron) spectrometer inethanol (95%).

TLC was performed on precoated aluminum sheets of silica gel 60 F₂₅₄(Merck), visualization of products being accomplished by UV absorbancefollowed by charring with 5% ethanolic sulfuric acid with heating;phosphorus-containing compounds were detected by spraying with Hanesmolybdate reagent (Hanes et. al., Nature, 154, 1107-1112, 1949). Columnchromatography was carried out on silica gel 60 (Merck).

High-performance liquid chromatography (HPLC) studies were carried outon a Waters Assoc. unit equipped with a model 616 pump system, a model600S system controller, a model 996 photodiode array detector and aMillennium data workstation. The column was a reverse phase analyticalcolumn (Macherey-Nagel, C₁₈, 150×4.6 mm, 5 μm) protected by a prefilterand a precolumn (Nucleosil, C₁₈, 5 μm). The compound to be analyzed waseluted using a linear gradient of 0% to 80% acetonitrile in 50 mMtriethylammonium acetate buffer (pH 7) programmed over a 40 min periodwith a flow rate of 1 ml/min and detection at 260 nm.

Evaporation of solvents was carried out on a rotary evaporator at 40° C.or lower under reduced pressure. Dichloromethane and 2-mercaptoethanolwere distilled over calcium hydride and acetonitrile was dried overphosphorus pentoxide. Anhydrous N,N-dimethylformamide (Fluka) was usedas supplied. All solvents used in reactions involving trivalentphosphorus compounds were degased by an argon stream before use. Allreactions were carried out under rigorous anhydrous conditions under anargon atmosphere.

Tris(pyrrolidino)phosphine was prepared as described by Wiesler at al.(Wiesler et al., Methods in molecular biology: Protocols for nucleotidesand analogs (S. Agrawal Ed.), Humana Press Inc., Totowa, N.J., Vol. 20,1991-206, 1993. d4T and ddA were supplied by Sigma (D1413) and Fluka(36769) respectively and were dried over P₂ O₅ under reduced pressure arRT prior to use. Sublimed 1-H-Tetrazole was purchased from Sigma andused as supplied. Elemental sulfur and trimethylacetic anhydride werepurchased from Aldrich, tertbutyl hydroperoxide (3M in toluene) fromFluka.

EXAMPLE 15 2-Mercaptoethyl-1-pivaloate

The title compound was prepared by adapting a method described by Mileset al., J. Chem. Soc., 817-826, 1952. Trimethylacetic anhydride (5.8 ml,28.5 mmol) was added dropwise to a mixture of 2-mercaptoethanol (2.0 ml,28.5 mmol) and sulfuric acid in acetic acid (0.09 ml, 10%, v/v) at 0° C.The solution was heated for 1h at 60°-65° C. and stirred during 3h atroom temperature. After dilution with diethylether (40 ml), the reactionmixture was neutralized with saturated NaHCO3 solution (10 ml), theorganic layer was separated, washed with water (3×10 ml), dried oversodium sulfate, filtered and evaporated. The residue was distilled underreduced pressure (bp₁₃ =63°-64° C.) to yield 2.2 g (13.7 mmol, 48%) of 4as a colorless oil.

R_(f) 0.64 (ethyl acetate/toluene 2:8);

¹ H NMR (CDCl₃) δ1.17 (s, 9H, tBu), 1.43 (t, 1H, SH, J=8.5 Hz),2.66-2.75 (m, 2H, SCH₂ CH₂), 4.14 (t, 2H, CH₂ CH₂ O).

EXAMPLE 16 General procedure for the preparation of thephosphorodithiolates S,S'-bis(O-pivaloyl-2-oxyethyl)O-2',3'-dideoxyadenosin-5'-yl phosphorodithiolate andS,S'-bis(O-pivaloyl-2-oxyethyl)O-2',3'-dideoxy-2',3'-didehydrothymidin-5'-yl phosphorodithiolate

The appropriate nucleoside (0.5 mmol) was dissolved either in a mixtureof DMF and dichloromethane (d4T, 1:3, 6 ml) or in DMF (ddA, 6 ml) bywarming the solution at 50° C. After cooling to room temperature, thesolution was stirred for 2h over 3 Å molecular sieve (0.5 g).Tris(pyrrolidino)phosphine 1² (120 mg, 0.55 mmol) was added, followed by1H-tetrazole in seven aliquots (7×50 μl of 0.5M tetrazole inacetonitrile, 0.175 mmol) at 3 min intervals. After stirring at roomtemperature for 15 min, 1H-tetrazole (5.2 ml 0.5M tetrazole inacetonitrile, 2.60 mmol) was added, immediately followed by the additionof the thiol 4 (243 mg, 1.5 mmol). The reaction mixture was stirred atroom temperature for 45 min and then cooled to -40° C.tert-Butyl-hydroperoxide (360 μl, 3M in toluene) was added and thereaction mixture allowed to warm to room temperature over 45 min. Thereaction mixture was concentrated under reduced pressure toapproximately 2 ml and diluted with dichloromethane (10 ml). The excessof oxidant was destroyed by the addition of Na₂ S₂ O₃ (10%, 5 ml). Theorganic phase was separated and the aqueous phase extracted twice withdichloromethane (2×10 ml). The combined organic layers were successivelywashed with brine (10 ml) and water (10 ml). The organic layer was driedwith sodium sulfate, filtered and concentrated to dryness under reducedpressure. Column chromatography of the residue on silica gel affordedthe title compounds.

EXAMPLE 16A S,S'-bis(O-pivaloyl-2-oxyethyl)O-2',3'-dideoxyadenosin-5'-yl phosphorodithiolate

85 mg, 0.14 mmol, 28% after chromatography eluent, stepwise gradient ofmethanol (3→5%) in dichloromethane!.

R_(f) 0.30 (methanol/dichloromethane 1:9);

¹ H NMR (CDCl₃) δ1.20 (s, 18H, tBu), 2.19-2.28 (m, 2H, 3'-H, 3"H),2.48-2.68 (m, 2H, 2'-H, 2"-H), 3.07-3.20 (m, 4H, SCH₂ CH₂), 4.29 (t, 4H,CH₂ CH₂ O, J=6.4 Hz), 4.30-4.48 (m, 3H, 4'-H, 5'-H, 5"-H), 5.3 (bs, 2H,NH₂), 6.31 (q, 1H, 1'-H, J=3.9, 6.5 Hz), 8.07, 8.35 (2s, 2H, 2-H, 8-H);

¹³ C NMR (CDCl₃) δ26.03 (C-3'), 27.05 (C(CH₃)₃), 30.42, 30.45 (2d, SCH₂CH₂, J_(p-c) 14 Hz), 32.16 (C-2'), 38.72 (C(CH₃)₃), 62.56, 62.58 (2d,OCH₂ CH₂, J_(p-c) 5 Hz), 67.93 (d, C-5', J_(p-c) 8 Hz), 79.20 (d, C-4',J_(p-c) 8 Hz), 85.51 (C-1'), 120.02 (C-5), 138.71 (C-8), 149.23 (C-4),152.82 (C-2), 155.48 (C-6), 177.95 (C═O);

³¹ P NMR (CDCl₃) 6 57.09 (s);

FAB MS (>0, G═T) m-e 604 M+H!⁺ ;

FAB MS (<0, G-T) m-e 602 M-H!; 474 OPS (SR) (OddA)!; 385 OPO(SR)₂ !;

UV (ethanol 95) λmax 259 nm (ε14900);

HPLC t_(R), 29.5 min.

EXAMPLE 16B S,S'-bis(O-pivaloyl-2-oxyethyl)O-2',3'-dideoxy-2',3'-didehydrothymidin-5'-yl phosphorodithiolate

98 mg, 0.17 mmol, 33% after column chromatography (eluentethylacetate/dichloromethane 3:7);

R_(f) 0.28 (dichloromethane/ethyl acetate 4:6);

¹ H NMR (CDCl₃) δ1.19, 1.20 (2s, 18H, tBu), 1.94 (d, 3H, thymine-CH₃,J=1.2 Hz), 3.09-3.21 (m, 4H, SCH₂ CH₂), 4.24-4.34 (m, 5H, CH₂ CH₂ O,5'-H), 4.37-4.48 (m, 1H, 5'-H), 5.03-4.29 (m, 1H, 4'-H), 5.91-5.93 (m,1H, 2'-H), 6.34-6.36 (m, 1H, 3'- H), 7.01-7.03 (m, 1H, 1'-H), 7.20 (d,1H, 6-H, J=1.1 Hz), 8.80 (bs, 1H, NH);

¹³ C NMR (CDCl₃) δ12.56 (thymine-CH₃), 27.08 (C(CH₃)₃), 30.51, 30.54(2d, SCH₂ CH₂, J_(p-c) 40 Hz), 38.76 (C(CH₃)₃), 62.59, 62.63 (2d, OCH₂CH₂, J_(p-c) 13 Hz), 67.15 (d, C-5', J_(p-c) 8 Hz), 84.15 (d, C-4',J_(p-c) 9 Hz), 89.58 (C-1'), 111.43 (C-5), 127.84 (C-2'), 132.86 (C-3'),135.48 (C-6), 150.69 (C-2), 163.55 (C-4), 177.94 (C═O );

³¹ P NMR (CDCl₃) δ57.29 (s); FAB MS (>0, G-T) m-e 1185 2M+H!⁺ ;

FAB MS (<0, G-T) m-e 1183 2M-H!; 591 M-H!; 463 OPS (SR) (Od4T)!; 385OPO(SR)₂ !;

UV (ethanol 95) λ_(max) 264 nm (ε7250);

Anal. Calcd for C₂₄ H₃₇ N₂ O₉ PS₂ : C, 48.63; H, 6.29; N, 4.73; S,10.82; Found: C, 48.65; H, 6.38; N, 4.73; S, 10.97.

HPLC t_(R) 29.6 min.

EXAMPLE 17 Stability studies of isostericS,S'-bis(O-pivaloyl-2-oxyethyl) O-2',3'-dideoxyadenosin-5'-ylphosphorodithiolate andO-(2',3'-dideoxyadenosin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl) phosphate

Certain kinetic studies comparing the compound of example 16A, i.e.,S,S'-bis(O-pivaloyl-2-oxyethyl) O-2',3'-dideoxyadenosin-5'-ylphosphorodithiolate, also designated as iso Bis(SATE)ddA! and itsisosteric compound of Example 9, i.e.,O-(2',3'-dideoxyadenosin-5'-yl)-O,O'-bis(S-acetyl-2-thioethyl)phosphate, also designated as Bis(SATE)ddAMP! were effected. The kineticwere studies were performed in culture medium (RPMI containing 10%heat-inactivated fetal calf serum) in order to evaluate the stability ofthe pronucleotides in the extracellular medium used for antiviralevaluation in cell culture systems, and in total cell extracts thatmimic the behavior of the compounds inside cells. The "on-line ISPRcleaning" HPLC method of Lefebvre et al., J. Med. Chem., 38, 3941-3950,1995, were used for the studies. The products resulting from thedecomposition were characterized by co-injection with authentic samplesand/or by coupled HPLC/Mass Spectroscopy. The kinetics of transformationof the two isomeric pronucleotides strongly differed according to themedium. In culture medium the first iso-SATE group was cleaved in 38.5hr whereas the first SATE group was cleaved in 165 hr. The secondiso-SATE group was cleaved in 5.8 hr whereas the second SATE group wascleaved in 46 hr. In total cell extracts, the first iso-SATE group wascleaved in 5.3 hr whereas the SATE group was cleaved in 1 hr.

EXAMPLE 18 Decomposition pathway of S,S'-bis(O-pivaloyl-2-oxyethyl)O-2',3'-dideoxyadenosin-5'-yl phosphorodithiolate, i.e. isoBis(SATE)ddA!, and S,S'-bis(O-pivaloyl-2-oxyethyl)O-2',3'-dideoxy-2',3'-didehydrothymidin-5'-yl phosphorodithiolate, i.e.iso Bis (SATE) d4T!

The proposed decomposition pathway for the compounds of Example 16a and16b, ie., S,S'-bis(O-pivaloyl-2-oxyethyl) O-2',3'-dideoxyadenosin-5'-ylphosphorodithiolate and S,S'-bis (O-pivaloyl-2-oxyethyl)O-2',3'-dideoxy-2',3'-didehydrothymidin-5'-yl phosphorodithiolate, alsodesignated as iso Bis(SATE)ddA! and iso Bis(SATE)d4T! is shown in FIG.9. This pathway was studied in conjunction with the kinetic studies ofExample 17. While we do not wish to be bound by theory, based upon theseresults it is presently believed that the decomposition pathway for theiso-SATE pronucleotide involves:

(a) carboxyesterase-mediated cleavage of the ester function leading to(A);

(b) nucleophilic attack of the liberated hydroxyl function on thephosphorus atom, forming the five-covalent intermediate (B);

(c) conversion of the intermediate (B) into the 2-mercaptoethylphosphorotriester (C);

(d) spontaneous elimination of episulfide, leading to the correspondingphosphorothiolate diester (D); and

(e) hydrolysis of the phosphorothiolate diester (D) into thecorresponding 5'-monophosphate by a similar mechanism (a-b-c-d) orfollowing the action of phosphodiesterases. Additionally, the hydrolysisof the iso-SATE pronucleotide may involve a direct nucleophilic attackon the phosphorus atom, leading directly to the phosphothiolate diester(D). Again while we do not wish to be bound by theory, we believe thismight explain the faster decomposition of the iso-SATE pronucleotidecompound to that of the SATE pronucleotide compound in culture medium.

EXAMPLE 19 Anti-HIV activity of mononucleosideS,S'-bis(O-pivaloyl-2-oxyethyl) phosphorodithiolates

The iso-SATE pronucleotides of Examples 16A and 16B were evaluated fortheir inhibitory effects on the replication of HIV-1 in CEM-SS and inthymidine-kinase deficient cell lines (CEM/TD). For comparison, theparent nucleosides ddA and d4T, and the corresponding bis(SATE)phosphotriesters bis(tBuSATE)ddAMP (the compound of Example 9) andbis(tBuSATE)d4TMP, were evaluated in the same experiments. The resultsare shown in FIG. 10. In the two cell culture systems, the anti-HIV-1activities of the tBu(iso)SATE pronucleotide were similar to those oftheir corresponding tBu(SATE) pronucleotides, both types of isomericpronucleotides being more potent inhibitors than the parent compoundddA. The d4T derivative showed high inhibitory effects inthymidine-deficient (TK) CEM cells while, as expected, the d4T is weaklyactive in this cell line. This data clearly demonstrates that theisoSATE pronucleotides that were evaluated could act as efficientprodrugs forms of the 5'-monophosphates, circumventing the firstactivation step by cytosolic kinases.

What is claimed is:
 1. A compound having formula Ia:

    RS--P(═O) (QR)--Nu                                     (Ia)

in which: R is --(CH₂)n-W--X; X is --C(═Z) (Y) or --S--U; Z is O or S; Wis O or S; Q is O or S; Y and U are, independently, an alkyl, aryl orsaccharide radical; n is 1 to 4; and Nu is a biologically activecompound or the dephosphorylated residue of a compound which isbiologically active when it bears a phosphate or phosphonate group. 2.The compound of claim 1 wherein X is --S--U and U is (CH₂)_(n') --X¹where X¹ is H, OH, SH or NH₂ and n' is 1 to
 4. 3. The compound of claim2 wherein R is --(CH₂)₂ --S--S--(CH₂)₂ --OH.
 4. The compound of claim 1wherein X is --C(═Z)Y and Y represents CH₃ or tBu.
 5. The compound ofclaim 4 wherein R is --(CH₂)_(n) --S--C(═O)--CH₃ or (CH₂)_(n)--S--C(═O)--tBu with n=1 or
 2. 6. The compound of claim 1 wherein Nu isa nucleoside.
 7. The compound of claim 6 wherein Nu is a2',3'-dideoxynucleoside or 2',3'-didehydronucleoside.
 8. The compound ofclaim 7 wherein Nu is a 5' residue of dideoxyuridine, dideoxythymidine,dideoxycytidine, or 3'-azido-2',3'-dideoxythymidine.
 9. The compound ofclaim 1 wherein Nu is a carbonucleoside, phosphonucleoside, or anacyclonucleoside.
 10. The compound of claim 9 wherein Nu is amethoxyalkylpurine or methoxyalkylpyrimidine, or of formula CH₂--O--alkylpurine or CH₂ --O-alkylpyrimidine.
 11. The compound of claim10 wherein Nu is a 3-hydroxy-2-methoxypropylpurine or3-hydroxy-2-methoxypropylpyrimidine radical of formula, of formula --CH₂--OCH(CH₂ OH)--CH₂ -purine or --CH₂ --OCH(CH₂ OH)--CH₂ -pyrimidine or a2-methoxyethylpurine or 2-methoxyethylpyrimidine radical, of formula--CH₂ --O--C₂ H₄ -purine or --CH₂ --O--C₂ H₄ -pyrimidine.
 12. A processfor the preparation of a compound of claim 1 comprising the steps ofappending protecting groups to said R groups and then removing saidprotecting groups to provide said compound.
 13. The process of claim 12wherein a compound of formula (II):

    O.sup.- --P(═O) (O.sup.-)--Nu                          (II)

is reacted a compound of formula (III):

    X--S--(CH.sub.2).sub.n --OH                                (III)

where X is protected, to provide said protected compound of formula (I);and said protected compound of formula (I) is deprotected.
 14. Theprocess of claim 13 wherein the reaction between the compounds offormulas (II) and (II) takes place in the presence of a condensing agentin pyridine.
 15. The compound of claim 1 wherein Y or U are substitutedwith an OH, SH or NH group.
 16. The compound of claim 1 wherein n is 1or 2.